Outer-Loop Control Design and Simulation Handling Qualities Assessment for a Coaxial-Compound Helicopter and Tiltrotor

This paper describes the development of full flight envelope dynamic inversion outer-loop control laws used to control airspeed and flight path for two Future Vertical Lift-relevant rotorcraft configurations - a lift offset coaxial helicopter with a pusher propeller and a tiltrotor. The outer-loop control laws for both aircraft include a control allocation scheme to account for redundant controls and reduce pilot workload. A piloted simulation experiment was conducted at the Penn State Flight Simulator facility using a series of high-speed handling qualities demonstration maneuvers to evaluate the handling qualities of the control laws. Overall, the outer-loop control laws for both coaxial-pusher and tiltrotor aircraft were assigned Level 1 handling qualities for the Break Turn and High-Speed Acceleration/Deceleration tasks, and reduced pilot workload over previously developed inner-loop control laws. The outer-loop control laws also improved performance and reduced pilot workload in a formation flying task developed for this experiment. The coaxial-pusher outer-loop control laws received borderline Level 1/Level 2 ratings for the Pitch Attitude Capture and Hold and Sum-of-Sines Tracking tasks, while the tiltrotor outer-loop control laws (with their increased value of pitch attitude dropback) received Level 2 ratings.